The invention relates to a wood substitute material for wood-encased pencils, such as lead pencils, colour pencils or cosmetic pencils with colour-releasing leads as well as various other types of pencils with leads made, for example of eraser material, etc., as well as to the use thereof.
The wood of the pencil enveloping the lead is replaced by the wood substitute material.
Wood-encased pencils in which the lead is surrounded or sheathed by naturally grown wood have long been known. In recent years the price of quality high-grade woods has increased owing to the lack of availability of wood, which has a direct effect on pencil production costs. In addition, comparatively large natural woods deposits are being consumed for the production of pencils.
For this reason it has already been attempted for years in the field of other trades to replace natural woods with wood substitute materials that are more cost effective and preserve the natural appearance of wood.
One type of wood substitute materials are ‘wood plastic composites’, which are thermoplastically processable materials with different fractions of wood, plastics materials and additives and are processed by thermoplastic forming processes, such as extrusion, injection moulding or pressing.
The additives optimise the performance characteristics required for the respective intended use and influence them considerably. For example adhesion promoters for improving the wood-plastic bond, waxes for ensuring processability, pigments for creating colour and means for ensuring the UV-, weather-, insect- and fungus-resistance are thus used.
Fields of application include, inter alia, patio floorings, plant boxes, claddings, ground surfaces, furniture or internal fittings in the automobile industry.
In addition to other properties, the wood substitute materials currently available on the market have been optimised in such a way that they exhibit the highest possible strength properties, such as bending strength or abrasion resistance.
However, wood substitute materials of this type are not suitable for the replacement of wood in wood-encased pencils, or are only suitable to a limited extent since pencils of this type either cannot be sharpened with a commercial conventional hand-held sharpener or else only with difficulty.
Foamed plastics materials or inorganically filled plastics materials are also known that act as wood substitute materials.
Foamed plastics materials have a low modulus of elasticity and are therefore normally very resilient. Owing to this high resiliency foamed plastics materials are les suitable as wood substitute materials for pencils since, with a resilient enveloping of a conventional lead, the necessary supporting effect for the lead is lacking and the lead may break when the pencil is used. Although this can be prevented by a correspondingly resilient configuration of the lead, the lead then exhibits poorer writing properties however.